Abstract:

Traditional stress dilatancy theories fail in unified treatment of sand responses. As a granular material, the mechanical behavior of sand is both density dependent and stress dependent. The ignorance of the dependence on material internal state in the widely cited form of stress dilatancy theory results in a negative feature in sand modeling. That is, a single sand with different initial states is treated as different materials. Consequently, multiple sets of model constants are calibrated for a single sand, and the influence of changes in material state during loading cannot be accurately traced. The state-dependent dilatancy (Li & Dafalias, 2000), in which the dilatancy is defined as a function of material internal state as well as of external stress state, offers a remedy to the problems associated with the stress dilatancy theory, and, in conjunction with the concept of critical state, provides a unified modeling framework for sand. A systematic investigation, including laboratory tests, theoretical modeling, and numerical analysis, was carried out to verify the state-dependent dilatancy theory. In the experimental investigation, a series of laboratory tests, including triaxial compression and extension tests, torsional shear tests, and resonant column tests, was performed to investigate the comprehensive behavior of Leighton Buzzard sand under various loading and drainage conditions. Based on the test results, a unified sand model, established within the framework of the state dependent dilatancy and the concept of critical state, was calibrated. The responses of sand in tests were simulated with this calibrated model. The verified model w ith the calibrated model constants was then used in a fully coupled finite element procedure to investigate the shear band formation in plane strain condition. The insights gained include the physical mechanisms of shear band formation in sand, the differences between global deformation and local deformation, and the influence of soil density on shear band formation.